As a multicolor or single-color image forming technology, this technology has been known in that an ink sheet containing a sublimable dye is in contact with an image-receiving layer of a image-receiving element and is heated by a thermal head, etc. so that the sublimable dye is transferred imagewise to the image-receiving layer.
In such the transferred image forming technology, the sublimable dye employed in the ink sheet plays an important roles, and image preservation quality is not sufficient from the conventional sublimable dye. As for improving this problem it is disclosed in Japanese Patent Publication Open to Public Inspection Nos. 59-78893, 59-109394, 60-2398 etc. that a metal chelate is formed by allowing a metal ion-containing compound (metal source) to react with a thermally transferable dye which is capable of chelate reaction (post chelate dye) to form a dye image.
It has been known that the image preservation quality of the post chelate sublimable dye image is improved as a chelation ratio becomes higher which is obtained by allowing a post chelate dye supplied from the ink sheet to react with the metal source in the image-receiving layer.
As a method to increase the chelation ratio, a technology has been proposed in that an image formed by transfer is treated at high temperature employing a thermostat or another heating device (Japanese Patent Publication Open to Public Inspection No. 4-89292 and Japanese Patent Application No. 5-258397). However, in this method, there is a disadvantage since another device is required in addition to a thermal transfer printer and further two steps-working is required for forming image with inferior handling. In this method, cost becomes higher since a sheet form protective material is necessary attaching between the image receiving sheet and roller and press plate to avoid contamination of the roller and press plate by dye transfer in the heating procedure.
A method heating the image formed by thermal transfer recording, a method employing thermal head is proposed. For example, it is disclosed in Japanese Patent Publication 4-55870, employing a sublimation transfer paper having dye areas of each color and an area having no coating, a transferred image receiving sheet is heated again through the non-coated area by means of a thermal head after the dye transfer. This method is advantageous because the re-heating is carried out within a same apparatus as the thermal transfer recording apparatus.
In case that the re-heating is carried out employing a thermal head with the same applied energy as that is applied when dye transferring with the maximum density, the image receiving layer or support is deteriorate so that an original surface characteristics of the image receiving sheet is lost, uneven band image appears at the high density area or sticking occurred at worst due to reducing the slippability between the image receiving layer and ink layer or back side of ink sheet and thermal head, because an excess energy all energy for dye transfer is used for the re-heating. For this reason the applied energy is set at lower condition than that gives maximum density of dye transfer. When the applied energy is reduced to avoid the phenomenon mentioned above, chelation of the post chelate dye is not performed sufficiently and the preservation quality of the obtained image becomes reduced.